Endocrine Abstracts

Introduction: Radioiodine (RAI) is safe and effective but further information to predict outcomes, specifically treatment failure and residual symptoms following treatment of hypothyroidism, may help improve outcomes.

Methods: Retrospective, observational, single-centre study. Electronic medical record review (n= 664) and patient questionnaire (n= 174).

Results: Complete cohort: Analysis of outcomes limited to 555 patients receiving first dose of 400 MBq. 77.1% hypothyroid, 5.6% euthyroid, 16.8% hyperthyroid and 3 deceased at 1 year. Treatment failure was associated with higher TRAb (OR 1.8, P=0.01 for TRAb above median); the only significant predictor in a model including gender, age, pre-treatment fT4 and TSH. Pre-treatment with thionamides (51.8% of cases) was associated with a 2.9-fold increased risk of treatment failure (P<0.001). Thionamide after RAI (28.0%) carried a 2.3-fold increased risk of failure (P<0.001).

Questionnaire: 31% were current smokers at the time of RAI. Thyroid eye disease was present in 10.9% prior to treatment and in 19.0% after. Median weight change was +6.0 kg (IQR 3.6–7.4), with multiple regression identifying only higher pre-treatment fT4 as a predictor of weight gain (P=0.03). 59.6% reported weight gain (A), 51.8% required more sleep since RAI (B), 44.4% felt less energetic (C), 41.8% felt slower mentally (D) and 42.4% reported more difficulties with memory (E). Logistic regression identified female gender (A,B,C); higher levothyroxine dose (A,B); and lower fT4 (A,D,E) as independent predictors of greater symptoms following RAI. 79.4% would recommend RAI to a friend.

Conclusions: • TRAbs may be a useful tool in stratifying radioiodine dose.

• Thionamide therapy may increase treatment failure risk, independently of disease activity.

• Patients are largely satisfied with RAI despite high prevalence of symptoms.

• Greater symptoms in those with lower fT4 despite larger dose of levothyroxine raise questions regarding optimal replacement therapy.